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Comparative studies of natural groups of organisms

(c) Asymmetric flowers Floral diagrams
These flowers have no plane of symmetry, A floral diagram is a diagrammatic
they cannot be divided into two equal halves representation of the transverse section of
in any plane; this is because their parts are a flower. It shows a plan of the flower as
spirally arranged, and good examples are viewed from above with each of its floral
flowers of Cacti, Canna indica, and ginger. whorls represented by a series of centric
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cycles showing their number, arrangement,
Methods of representing floral structure relative position and fusion. The axis of
Flower features can be represented to the inflorescence is represented by a small
reveal the arrangement and relationship of cycle at the top of the diagram, which is
the parts using three methods. These are then regarded as the posterior position
a half-flower diagram, floral formula, and of the flower and bracts, if present. In
floral diagram. principle, floral diagrams are never
labelled, but standard symbols are used
A half flower diagram (Figure 3.38b). Although such symbols
This is a schematic representation of may not be representing physical structures,
a flower cut longitudinally along the they carry additional floral information,
median plane in relation to the main stem such as symmetry and orientation. Floral
to provide an elevation view of the flower. diagrams are useful in the identification
Normally, in regular flowers, cutting along of flowers, comparison of angiosperm
this plane will result into two identical and taxa, reconstruction of fossil flowers, as
opposite halves of the flower. A half cut well as in understanding the ontogeny and
flower diagram shows exactly how the phylogeny of angiosperms.
floral parts are arranged in relation to each
other (Figure 3.38a).

Plant axis
Anther
Petal
Filament
Style Sepal

Ovary Petal
Sepal
Stamen

Figure 3.38: Representation of flower features (a) a half-flower diagram (b) floral symbols

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